Many sealing mechanisms have been created including sealing mechanisms such as those used in “Foam-In-Bag”, “Air-In-Bag” and “Food (or other Product types)-In-Bag” manufacturing devices. Many endeavor to use a sealing wire, heated by electrical resistance, which rolls or drags over the material being sealed. Other sealing techniques have been attempted, including the use of hot melt glues, pressures sensitive adhesives, pressure sensitive co-adhesives, hot air jets, hot metal rollers and mechanical crimping.
Examples of heated wire “Air-in-bag” embodiments are seen in U.S. Pat. Nos. 6,598,373 and 5,942,076 which are incorporated herein by reference.
One sealing approach relative to a foam-in-bag device is represented by U.S. Pat. No. 5,679,208. In one commercialized (foam-in-bag) embodiment of U.S. Pat. No. 5,679,208 a round, 10-mil diameter, Nichrome material sealing wire is wrapped around the outside diameter of a rigid nip roller opposing a rubber nip roller. The sealing substrate, underneath the wire, is a hard plastic material as in “VESPEl” plastic, that is selected on the belief it can resist the extreme heat of the sealing wire. The sealing wire is wrapped around the roller, but the ends are separated, each end being one contact point for the flow of electrical current.
As the nip rolls turn, the electrically heated wire turns with the rigid roller, essentially rolling over an open edge of the bag, forming the edge seal during its brief contact period with the film as the film passes through the nipped section.
A problem associated with the '208 patent approach is that it requires a rotating electrical contact to supply power to the edge seal wire. Since the edge seal wire is rotating with the nip roll, direct wire connections from the edge seal wire to the non-rotating control board presents the potential for wind up and breakage after a few revolutions. This problem is addressed with a rotating electrical union, which is quite expensive and has many failure modes of its own. Also, maintenance (e.g., heater wire replacement) is difficult with this embodiment as can be seen by the high finger dexterity requirement associated with removing and replacing wires on its substrates. In addition, even with a highly skilled person with good dexterity the switching out of a defective wire for a new one is time consuming and thus also undesirable to a user from a manufacturing “down time” efficiency standpoint.
An additional edge sealer embodiment is described in U.S. Pat. No. 6,472,638 showing a snap on edge sealer that is a “drag seal” embodiment wherein a pair of downstream drive rollers pull the film past the clipped on edge sealer. This avoids having the complexity of maintaining electrical contact relative to a rotating heater wire support structure and a non-rotating support. In a commercialized embodiment of the '638 patent, the snap-on unit, called an edge seal card, can be replaced without using any tools within a few minutes. This commercialized embodiment of a drag sealer features a 10-mil, round Nichrome wire attached at the face of a thin “Delrin” card, which is machined to the same 2.5-inch radius as a receiving nip roll. A segment of the wire, of about ¼ inch long, is exposed on the edge of the card, but is covered by a layer of 3-mil Teflon tape. The Nichrome wire becomes a sealing element through electrical resistance heating. The exposed wire segment is placed in pressure contact with the rubber nip roll, and melts the film when it gets hot enough. The drive action of the two nip rolls drags the film past the hot wire, which is an example of a drag seal arrangement. A disadvantage of this commercialized embodiment of the '638 design is its short life in comparison to other designs. Even though replacement is easy and quick, the noted snap-on edge sealer is often able to only run for a few film rolls before having to be removed.
A further difficulty associated with the prior art designs is seen in the difficulty of forming and maintaining good seal production as opposed to weak or defective seals due to improper bonding temperature or surface contact, or too much contact or heat application and a resultant improper ribbon cutting (in situations where ribbon cutting is not an intended result).
Applicants believe that the following are some reasons for the failure modes in the '638 commercialized embodiment design:
1. The seal wire melts into the substrate, as in “Acetal” or “Delrin” material, causing it to lose sealing power into the substrate, leading to poor seals.
2. The seal wire burns a hole in the Teflon tape that covers it, causing the unit to make bad seals.
3. In general, seal quality is not consistent, causing the machine operator to make frequent adjustments to the temperature settings or attempts to repair the edge seal card in order to maintain seal quality.
4. The edge seal cards are not interchangeable, and the machine operator has to adjust its temperature setting every time a new one is installed.
5. When the 10-mil Nichrome wire does fail there is no easy way to replace it, which is frustrating to operators because the wire only costs a few cents while the entire card assembly is much more expensive.
6. The rubber roll will gradually wear a matching radius into the edge of the plastic edge seal card in contact with it, reducing its usefulness over time.
7. The cables that connect the edge seal card to the plug-in connector panel, frequently get caught in the nip rolls or in the sealing jaws.
The snap-on drag sealers of the '638 patent represent sealing devices that are intended to be used to seal without cutting the film (although it is a difficult task with this prior art design to maintain a good strong seal without, at the same time, cutting through one or more layers of the film); or as an edge sealer that both seals and cuts the film. For foam-in-bag embodiments where it is desirable to form gas escape vents in or adjacent an edge seal, cutting of a layer of the film is one way to produce a vent for the release of pressure. For example, a commercialized embodiment of '638 patent includes a second edge seal card, with the sealing wire positioned to contact one layer of the bag film just before it enters the roller contact zone. When this wire is powered with sufficient energy, it will cut a slit in the moving web to produce a vent inside of the edge seal in the transverse direction. The length of the vent slit, and its gas flow capacity, can be controlled by adjusting the power on time of this wire. The commercialized embodiment of the “roller seal” described above for the '208 patent features a power lowering cycle to prevent a seal formation along a section of the overall seal length, which no seal formation vent is used to vent gases.